Discharge pressure estimation for compressor

ABSTRACT

A compressor has a controller which is provided with current information for a current passing into a motor associated with the compressor. The compressor includes a compressor pump unit driven by the motor, and a discharge line. The controller is programmed to utilize the current information to predict a discharge pressure at the discharge of the compressor.

BACKGROUND

This application relates to the use of motor current in a compressor to estimate a discharge pressure.

Compressors are an integral part of any refrigerant system. Modern compressors are provided with a large number of increasingly complex controls which take in data from any number of locations within an associated refrigerant system, and then develop ways to control the compressor most efficiently. One piece of data that is required is the discharge pressure of the compressor. Thus, a discharge pressure sensor is typically incorporated into modern systems.

Another competing factor in modern compressors is to lower cost. Each added component requires additional cost, and thus the elimination of a component would be desirable.

SUMMARY

A compressor has a controller which is provided with current information for a current passing into a motor associated with the compressor. The compressor includes a compressor pump unit driven by the motor, and a discharge line. The controller is programmed to utilize the current information to predict a discharge pressure at the discharge of the compressor.

These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows a refrigerant system.

FIG. 2 is a graph of current versus discharge.

FIG. 3 is a brief flow chart of this invention.

DETAILED DESCRIPTION

FIG. 1 shows a refrigerant system 20 incorporating a compressor 22 provided with an electric controller 32. Power 34 passes through the controller to the compressor 22 to drive a motor 51, which drives a compressor pump unit 50. The compressor pump unit 50 may be a scroll compressor, or may be any other type of compressor.

A suction line 152 leads into a sealed compressor chamber, and to the compressor pump unit 50. The suction pressure refrigerant is compressed and then delivered to a discharge line 52. As mentioned above, it is desirable to know the pressure at the discharge 52.

Suction pressure is also an important variable which is typically utilized in modern compressor controls. A suction pressure sensor 23 is shown schematically on the suction line 152. This sensor could be at any number of other locations, and the entire structure of the compressor 22 is shown schematically. Downstream of the compressor 22 is a condenser 24. Downstream of the condenser 24 is an expansion device 28, and then an evaporator 30. Refrigerant passes from the compressor 22, through the condenser 24, the expansion device 28, the evaporator 30, and then back to through the suction line 152 to the compressor 22.

The controller 32 takes measurements from an inverter of at least current passing to the motor 51. In addition, the controller 32 may receive information from the suction pressure sensor 23. Many compressor motors are fixed speed, and thus the controller 32 will know the speed. If the motor 51 can operate at several speeds, that information will also be sent to controller 32.

A temperature sensor 26 may be associated with the condenser 24. The temperature sensor could be on a condenser return bend, or if the condenser is a microchannel heat exchanger, in the return header.

FIG. 2 shows a relationship between current heading to the motor 51 and the discharge pressure. The varying curves would represent a change in discharge pressure with a change in current at different speeds.

The curves are shown as examples only, and the actual current versus discharge pressure curves would be developed for each compressor 22 which would utilize this invention. However, it is known that there is a relationship between discharge pressure and current.

Further, one may fine-tune this determination by adding suction pressure to provide more accurate estimates of the discharge pressure. Further, a temperature at the motor 51 can also be sent to the controller 32, and provide further fine-control over the estimate.

However, for purposes of the broadest aspects of this invention, all that would be necessary is to know current, and then to estimate discharge pressure. In this manner, the discharge pressure can be utilized by the controller 32 to control operation of the motor and compressor for any number of other applications.

At the same time, and as shown in FIG. 3, while the controller 32 is estimating the pressure P_(DC) or the discharge pressure based on current, the controller is also estimating a discharge pressure P_(DT), or one based upon the temperature information from the condenser temperature sensor 26. These can be compared. If the two estimated pressures are off by more than a predetermined amount, then a determination can be made that the system may be low on charge, or there could be something mechanically wrong with the compressor. Thus, as shown, some diagnostic warning can come from this comparison.

Although an embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention. 

1. A compressor comprising: a controller provided with current information for a current passing into a motor associated with said compressor, said compressor including a compressor pump unit driven by said motor, and a discharge line; and said controller being programmed to utilize said current information to predict a discharge pressure at the discharge of the compressor.
 2. The compressor as set forth in claim 1, wherein a suction pressure sensor provides suction pressure information to said controller.
 3. The compressor as set forth in claim 2, wherein a temperature at the motor is utilized to fine-tune the discharge pressure estimate.
 4. The compressor as set forth in claim 1, wherein said controller also takes in information from a location remote from said compressor and utilizes said information to calculate an alternative discharge pressure estimate, and said alternative discharge pressure estimate being compared to said discharge pressure estimate based upon current, and an indication of a potential problem being made should said two pressures differ by more than a predetermined amount.
 5. The compressor as set forth in claim 1, wherein the controller is provided with curves correlating current with discharge pressure and these are utilized to calculate the discharge pressure. 